In the manufacture of finished rubber goods, rubber slabs (large sheets of rubber) are often intentionally stacked on pallets for interim storage and/or transportation before the next manufacturing step. Such slabs of rubber have a tendency to stick together during storage. This problem becomes more serious at higher storage temperatures and with longer storage periods. The problem with sticking is also more frequently encountered in cases where a large number of rubber slabs are piled on top of each other. This problem can be so serious that it is virtually impossible for workers to pull apart rubber slabs that are stuck together. In such cases, the rubber slab is non-processable and sometimes even becomes waste product. Similar problems with sticking are also encountered with uncured rubber compounds that are in the form of pellets or granules.
To overcome this problem, slabs and pellets of rubber are generally treated with slab dips or pellet dips to inhibit the tendency of the rubber to stick together. Conventional slab dips and pellet dips normally contain clay or some other inorganic powder. The inorganic powder coats the surfaces of the rubber and provides a physical barrier or partition that keeps the rubber in the individual slabs or pellets from coming into contact with rubber in other slabs or pellets. However, the use of such conventional slab dips and pellet dips can lead to undesirable dusting problems in plant work areas. More significantly, the residual inorganic powders that remain in finished rubber goods can be detrimental to ultimate rubber properties. For instance, inorganic powder particles can serve as the nucleus for cut or tear growth in the finisher rubber article.
Syndiotactic 1,2-polybutadiene (SPBD) is a thermoplastic resin which can be utilized in making films, fibers and molded articles. For example, U.S. Pat. No. 4,394,473 and U.S. Pat. No. 4,957,970 disclose the use of SPBD in making bags and packaging. It can also be blended into elastomers, such as polydiene rubbers. Because SPBD contains double bonds which are attached in an alternating fashion to its backbone, it can be cocured with the rubbers in such blends. In fact, SPBD/rubber blends provide a unique combination of properties which make them useful in various tire compounds.
U.S. Pat. No. 4,790,365 discloses that incorporation of SPBD into rubber compositions which are utilized in the supporting carcass or innerliner of tires greatly improves the green strength of those compositions. Electron beam precure (microwave precure) is a technique which has gained wide commercial acceptance as a means of improving the green strength of synthetic elastomers which are used in building tires. However, electron beam precure techniques are costly. The incorporation of SPBD into blends of such synthetic elastomers can often improve green strength to the degree that electron beam precure is not required. The incorporation of SPBD into halogenated butyl rubbers which are utilized as the innerliner compositions for tires also greatly improves the scorch safety of such compositions. U.S. Pat. No. 4,274,462 disclosed that pneumatic tires having improved resistance against heat buildup can be prepared by utilizing SPBD fibers in their tread-base rubber.
According to U.S. Pat. No. 4,790,365, the SPBD utilized in making the supporting carcass for tires has a melting point which is within the range of 120.degree. C. to 190.degree. C. and that it is preferred for the SPBD utilized in making the supporting carcass to have a melting point which is within the range of 150.degree. C. to 165.degree. C. The SPBD utilized in making tire innerliners has a melting point which is within the range of 120.degree. C. to 160.degree. C. and preferably has a melting point which is within the range of 125.degree. C. to 150.degree. C. The melting points referred to herein are minimum endotherm values determined from DSC (differential scanning calorimetry) curves.